The present invention relates to a punching method and a punching system that form strip portions by punching a metal plate via shearing, and particularly to a punching method and a punching system that are suitable for forming narrow strip portions.
The rotor of a permanent magnet synchronous motor has a rotor body with through-holes. A permanent magnet is inserted in each through-hole. The rotor body is formed by laminating core plates, which are a number of magnetic steel plates. In this structure, to reduce leakage flux, the permanent magnets are preferably arranged in the outer circumferential portion of the rotor to be close to the stator. This improves the operating efficiency of the motor. To arrange the permanent magnets in the outer circumferential portion of the rotor, the width of the parts of the steel plates between the through-holes and the outer circumference of the rotor, that is, the width of strip portions that extend along the outer circumference of the rotor, must be minimized.
However, such narrow strip portions are difficult to form. Typically, core plates are worked via shearing by a press to form through-holes. However, since narrow strip portions would be severed by the pressure of shearing, narrow strip portions are difficult to form. If through-holes were formed by laser beam machining in an attempt to form narrow strip portions, not only would the machining time be prolonged, but also the heat would be highly likely to sever the strip portions.
If through-holes were formed through cutting to form narrow strip portions, a longer time than in the case of the laser beam machining would be required. Also, wear of the cutting edges would lower the cutting accuracy.
Japanese Laid-Open Patent Publication No. 2012-115089 discloses a motor designed to improve the operating efficiency by reducing leakage flux without forming narrow strip portions. The structure of the disclosed motor includes a rotor core having a main body, which is a bulk body. The bulk body has recessed grooves on the outer circumference. Each groove receives a steel plate laminate, which is formed by laminating magnetic steel plates formed separately from the bulk body. A permanent magnet is provided between the bulk body and each steel plate laminate.
In the configuration of the motor disclosed in Japanese Laid-Open Patent Publication No. 2012-115089, the rotor core is constituted by the bulk body and the steel plate laminates, which are formed separately from the bulk body. This increases the number of components and complicates the structure. Further, a height difference is likely to be created between the bulk body and the steel plate laminates in the thickness direction. Such a height difference causes leakage flux, which results in a lowered motor efficiency.